With the word "PM2.5"______ heard and seen in our life, people become more and more concerned about air pollution.

Once we discover a mistake, we should not _____ it but correct it immediately, to create better conditions for economic development.

At the meeting they discussed three different ________to the study of math.

(2013·高考浙江卷)Eye doctors recommend that a child’s first eye exam ________ at the age of six months old.

I think you are at the end of your ________ this time and need to turn to Pro. Smith for advice.